efl = bfl

  • 17 February 2021
  • 4 replies
  • 1047 views

Hello,


Anyone knows how I can optimize my design, so the effective focal length is equal to the back focal length. I found something about using two OPTH operands with a DIFF operand in the merit function, but I'm not sure how I can implement this.


Maybe there is another way?


Thank you!


4 replies

Userlevel 7
Badge +2

Hi Rick,


Perhaps I didn't get your question, but I think your idea to use DIFF is right.


EFFL will give you the effective focal length, and TTHI (applied to the last surface thickness of your lens design) is possibly the back-focal length (depending where your image plane is).


Targeting the difference (DIFF) of the two should make them equal.


Let me know if this works for you.


Take care,


David

Hi David,


Thank you for your answer. It does seem that the THIC operand is not available in the Merit function editor. Do I have to use it somewhere else?

Userlevel 7
Badge +2

Hi Rick,


Sorry, the operand is TTHI. The BFL should be specified in both Surf1, and Surf2.


I've updated my post. I got confused with the Multi-Configuration operand haha.


Take care,


David

Ok, thanks for the clarification!

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